Explain to me why a switch is required?
The Main Contactor will open the high current circuit when the control coil power is opened. I trust it wont fuse closed during operation. If anything, it will fail open if the control circuit fails open. Understand my logic?

ummm, I ALWAYS put a switch on the pack. It's kind of basic - you can have any number of things go wrong, and the switch lets you pull the pack offline immediately. The race bikes all require it - a big honkin' red button switch. Dice runs Anderson connectors and the one right under his knee has one of those handles on it, so he can pull it in a disaster.

I mean, if nothing else, it makes sure you won't have any parasitic losses when you park it.

ummm, I ALWAYS put a switch on the pack. It's kind of basic - you can have any number of things go wrong, and the switch lets you pull the pack offline immediately. The race bikes all require it - a big honkin' red button switch. Dice runs Anderson connectors and the one right under his knee has one of those handles on it, so he can pull it in a disaster.

I mean, if nothing else, it makes sure you won't have any parasitic losses when you park it.

Explain to me why a switch is required?
The Main Contactor will open the high current circuit when the control coil power is opened. I trust it wont fuse closed during operation. If anything, it will fail open if the control circuit fails open. Understand my logic?

#1 Emergency purposes, (like a crash) to be able to quickly disconnect the battery pack. (in an emergency)
#2 Maintenance, to be able to "safely" trouble shoot, do maintenance or repairs on the bike. (without having to manually disconnect a battery cable)
#3 Storage, to protect your battery pack (from parasitic draws, like Ted said)

Mike, Can you move the last few threads to the Fight Club and start a thread Necessity of a mechanical kill switch!
I will argue till I'm blue in the face about how stupid that racing rule is. If I were racing, I would wire one in just because it was required, but I'm not racing.
Seriously though...
If my pack goes up in flames, how is pulling a plug or flipping a switch gonna help put the fire out? I don't believe it will do one bit of good in that situation. And if there is a short in the system somewhere, the fuses will blow before I even have time to think about flippin a switch or pulling a plug.
I've always lived my life a lil on the edge, and this is a risk I'm willing to accept. If you want to wire in another possible point of failure, another possible point of water induced short, or another possible point of unnecessary resistance, go for it! But I disagree and I'll suffer the consequences if I'm wrong. I'm good with that decision.

I still don't see the need. The way my system is set up, the main contactor's control cool is energized by the 12v Sevcon dc-dc, which is turned on by an isolated 12v Vicor dc-dc. If I flip the mechanical power switch to that system, the Sevcon dc-dc powers down along with main contactor. Absolutely no difference than what your suggesting to do.

Mike, Can you move the last few threads to the Fight Club and start a thread Necessity of a mechanical kill switch!
I will argue till I'm blue in the face about how stupid that racing rule is. If I were racing, I would wire one in just because it was required, but I'm not racing.
Seriously though...
If my pack goes up in flames, how is pulling a plug or flipping a switch gonna help put the fire out? I don't believe it will do one bit of good in that situation. And if there is a short in the system somewhere, the fuses will blow before I even have time to think about flippin a switch or pulling a plug.
I've always lived my life a lil on the edge, and this is a risk I'm willing to accept. If you want to wire in another possible point of failure, another possible point of water induced short, or another possible point of unnecessary resistance, go for it! But I disagree and I'll suffer the consequences if I'm wrong. I'm good with that decision.

I am not lookin' to fight, but your playin' with High Voltage & it's not just "all about you", think about the first responders. (in the case of a crash)

Look at it another way, OSHA mandates that all industrial machines have a "lockable" main power disconnect switch (located right at the main power source) in addition to "emergency kill switches". (located easily within reach of the operator)

* Since its a motor vehicle, maybe check with the NHTSA (National Highway Traffic Safety Administration)

Mike, Can you move the last few threads to the Fight Club and start a thread Necessity of a mechanical kill switch!
I will argue till I'm blue in the face about how stupid that racing rule is. If I were racing, I would wire one in just because it was required, but I'm not racing.
Seriously though...

Settle down, Sparky.

If you want to ignore a decade or so of EV design, it's your choice. I wouldn't consider running something with over 70VDC without a mechanical cutoff for the pack, and most everybody (no, everybody) I know who's built anything with that kind of voltage (ESPECIALLY for off-road use) uses one, but whatever. I have a 24yr old son, I'm used to being ignored. I'm also used to him admitting I was right when shit goes bad.